Polaris ATV Forum banner

1 - 7 of 7 Posts

·
Registered
Joined
·
2 Posts
Discussion Starter #1
So I have a 1995 polaris Xplorer 400 2 stroke and for some unknown reason its locking itself up when I crank it over. I bought it from a garage sale and the owner said it was seized but when I got it home it turned over no problem. After I cleaned the carb and checked all the fluids I had it firing until it locked up, I couldn't crank it over or use the pull cord so I pulled the clutch cover off to see if something had jammed in there and everything was fine. I wiggled the clutch and it unlocked itself and it would then pull over and crank over and almost get going. It has done this a few times on me and I'm stumped, I have not pulled the recoil off yet to investigate further. Any advice would be appreciated, did a compression test and it was sitting right at 110 psi. thanks
 

·
Premium Member
Joined
·
7,402 Posts
Not a 2-stroke guy but I know on some applications for starting purposes there is a cylinder pressure release. Once started it is closed and the engine has full compression. Some motors have such high compression they need these valves for starting.
 

·
Registered
Joined
·
4,807 Posts
I am a two stroke guy - it sounds like the engine seizes when it gets hot, as it cools down it can unlock, but the damage is done - it will get to the point it will no longer start and will need rebuilt.

The thing is you got to figure out why it seized; lack of coolant, fan not running, lack of oil mixed with the gas? those are the most common problems. If not seizing, a bad crank bearing perhaps. On the worse scenario side of the problem, the big end bearing on the rod has gone bad and needs replaced and shrapnel from the bearing has damaged the piston and cylinder - all caused by oil pump failure of some variety (lack of oil in the oil tank will cause the pump to fail) and the engine needs a complete rebuild - about $1500 in my shop for an engine that does not have engine case damage. On the least serious side of the problem; the piston seized due to an over heat problem and the engine only needs the cylinder honed and a new piston and rings installed - about $250 - $300

There is no compression release on the 400L
 

·
Premium Member
Joined
·
7,402 Posts
There you have it the MAN has spoken. I figured it was a pressure relief deal as I have only seen that on small two-strokes like chainsaws.
 

·
Premium Member
Joined
·
3,507 Posts
There you have it the MAN has spoken. I figured it was a pressure relief deal as I have only seen that on small two-strokes like chainsaws.
Yep, Latebird knows his stuff, so there is your answer.

There are automatic compression release systems on our 4 stroke machines too. I have a Kawasaki Bayou in the shop that has an external lever for the compression release and it's only 220cc. In this case the description was yelling at me that there was an engine problem. With the compression at 110, I would suspect a bearing issue. From what I have seen with the 2 strokes I have worked on once they seize the piston to the cylinder, it messes up the ring lands and scores the cylinder wall sot he compression goes way down. Either way, the engine has to be torn down to find the culprit.
 

·
Registered
Joined
·
2 Posts
Discussion Starter #6
the engine locks up when it is cold, and then releases when I jiggle the primary clutch and turns over just fine with no noise from the starter or anything. It could be a main bearing but is there any chance this has something to do with the starter and the Bendix locking up?
 

·
Registered
Joined
·
4,807 Posts
It's unlikely that the starter or Bendix is locking up - the starter is one part and the Bendix is another part - the starter is engaged to the Bendix 100% of the time, but the Bendix only engages with the flywheel when the starter motor is running. If the Bendix locked to the flywheel it would release and freewheel, but strange things have happened.

Usually a two stroke will overheat and the piston gets too large for the bore and it seizes against the cylinder wall stopping the engine - technically, the piston melts and welds itself to the cylinder - the cylinder is steel and the piston is aluminum so the weld is not strong - when the engine cools, the weld will break and depending on the severity of the seizure, the rings may not be stuck in their grooves and the engine will run again, but it usually has a loss of power and the engine becomes noisier than before due to increased clearance or the rings contacting aluminum stuck to the cylinder wall. In some cases, a rod or main bearing may fail - the rod bearing is a roller bearing and the main bearings are ball bearings - either one can suffer a failure and cause the engine to lock - in most cases of bearing failure, turning the crankshaft backwards (clockwise from the LH clutch side) can unlock the bearing and it may have to rotate many times before the defect causes it to lock again, but it is not as common a cause as piston seizure.

Keep us posted on what you discover.
 
1 - 7 of 7 Posts
Top